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          生产者消费者模型多线程实现
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        <h2 id="生产者消费者模型实现"><a href="#生产者消费者模型实现" class="headerlink" title="生产者消费者模型实现"></a>生产者消费者模型实现</h2><p>​    生产者消费者问题是操作系统中典型的同步互斥问题。</p>
<p>本实验用多线程实现。</p>
<p>实验要求，用C实现经典同步问题：</p>
<ol>
<li>一个大小为10的缓冲区，初始状态为空。 </li>
<li>2个生产者，随机等待一段时间，往缓冲区中添加数据，若缓冲区已满，等待消费者取走数据之后再添加，重复10次。</li>
<li>2个消费者，随机等待一段时间，从缓冲区中读取数据，若缓冲区为空，等待生产者添加数据之后再读取，重复10次。</li>
</ol>
<p>那么分析要求，要实现生产者消费者对缓冲区操作互斥，生产者需要知道缓冲区是否已满，已满只能等待消费者取出之后才能对临界资源进行操作，同样消费者也要判断是否为空。由于有2个生产者与消费者进程，生产者与生产者，消费者与消费者之间也有读写互斥。</p>
<p>采用信号量机制进行进程间通信，在Linux系统中，一个或多个信号量构成一个信号量集合。每个P、V 操作不限于减1或加1，而是可以加减任何整数。在进程终止时，系统可根据需要自动消除所有被进程操作过的信号量的影响。</p>
<a id="more"></a>

<p>要求：</p>
<ol>
<li>缓冲区运用循环队列数据结构，头尾指针指定大小，读取数据，判断非空，大小为10。</li>
<li>利用随机函数rand()产生大写字母26个随机字符，作为生产者每次生产的数据，存放到缓冲区中。</li>
<li>使用shmget()系统调用实现共享主存段的创建， shmget()返回共享内存区的ID。对于已经申请到的共享段， 进程需把它附加到自己的虚拟空间中才能对其进行读写。</li>
<li>信号量建立采用semget()函数，同时建立信号量的数量。在信号量建立后，调用semctl()对信号量进行初始化 ，例如本实验中，可以建立两个信号量SEM_EMPTY、 SEM_FULL，初始化时设置SEM_EMPTY为10，SEM_FULL 为0。使用操作信号的函数semop()做排除式操作，使用这个函数防止对共享内存的同时操作。对共享内存操作完毕后采用shmctl()函数撤销共享内存段。</li>
<li>fork循环创建新进程。</li>
<li>一个进程的一次操作完成后，采用函数fflush()刷新缓冲区。</li>
<li>程序最后使用semctl()函数释放内存。</li>
</ol>
<p>显然实验如果用多进程编写，按照以上要求会十分困难，一般用pthread封装的线程库来编写，这样只需要关注生产者消费者核心的问题，而不用关注底层繁杂的接口调用(偷懒)。</p>
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class="line">182</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;stdlib.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;unistd.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;pthread.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;time.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">&lt;semaphore.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> BUFFSIZE 10</span></span><br><span class="line"></span><br><span class="line"><span class="comment">//条件变量</span></span><br><span class="line"><span class="keyword">pthread_cond_t</span> full = PTHREAD_COND_INITIALIZER;</span><br><span class="line"><span class="keyword">pthread_cond_t</span> empty = PTHREAD_COND_INITIALIZER;</span><br><span class="line"><span class="keyword">pthread_mutex_t</span> mutex = PTHREAD_MUTEX_INITIALIZER;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">BUFFER</span>&#123;</span></span><br><span class="line">    <span class="keyword">char</span> product[BUFFSIZE];</span><br><span class="line">    <span class="keyword">int</span> num;</span><br><span class="line">    <span class="keyword">int</span> head,end;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="comment">//信号量</span></span><br><span class="line"><span class="keyword">sem_t</span> semempty ,semfull;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">pTime</span><span class="params">()</span></span>&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">tm</span> *<span class="title">pt</span>;</span></span><br><span class="line">    <span class="keyword">time_t</span> tim;</span><br><span class="line">    tim = time(<span class="literal">NULL</span>);</span><br><span class="line">    <span class="built_in">printf</span>(ctime(&amp;tim));</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">char</span> <span class="title">retChar</span><span class="params">()</span></span>&#123;</span><br><span class="line">    <span class="keyword">int</span> temp = rand()%<span class="number">26</span>;</span><br><span class="line">    <span class="keyword">return</span> <span class="string">&#x27;A&#x27;</span>+temp;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> *<span class="title">producerOne</span><span class="params">(<span class="keyword">void</span> *args)</span></span>&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">BUFFER</span> *<span class="title">bo</span>;</span></span><br><span class="line">    bo = (struct BUFFER *) args;</span><br><span class="line">    <span class="keyword">while</span> (<span class="number">1</span>)&#123;</span><br><span class="line">        pthread_mutex_lock(&amp;mutex);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">while</span> (bo-&gt;num == BUFFSIZE)&#123;</span><br><span class="line">            <span class="comment">//满等待互斥锁</span></span><br><span class="line">            pthread_cond_wait(&amp;full,&amp;mutex);</span><br><span class="line">        &#125;</span><br><span class="line">        sem_wait(&amp;semempty);</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;当前工作进程为生产者1\n&quot;</span>);</span><br><span class="line">        <span class="keyword">char</span> c = retChar();</span><br><span class="line"></span><br><span class="line">        bo-&gt;end = (bo-&gt;end+<span class="number">1</span>)%BUFFSIZE;</span><br><span class="line">        bo-&gt;product[bo-&gt;end] = c;</span><br><span class="line">        bo-&gt;num++;</span><br><span class="line"></span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;生产字符为:%c\n&quot;</span>,c);</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;当前缓冲区数据个数为:%d\n&quot;</span>,bo-&gt;num);</span><br><span class="line"></span><br><span class="line">        pTime();</span><br><span class="line">        sem_post(&amp;semfull);</span><br><span class="line">        <span class="keyword">if</span>(bo-&gt;num == <span class="number">1</span>)&#123;</span><br><span class="line">            pthread_cond_signal(&amp;empty);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">//释放锁</span></span><br><span class="line">        pthread_mutex_unlock(&amp;mutex);</span><br><span class="line">        sleep(rand()%<span class="number">2</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> *<span class="title">producerTwo</span><span class="params">(<span class="keyword">void</span> *args)</span></span>&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">BUFFER</span> *<span class="title">bo</span>;</span></span><br><span class="line">    bo = (struct BUFFER *) args;</span><br><span class="line">    <span class="keyword">while</span> (<span class="number">1</span>)&#123;</span><br><span class="line">        pthread_mutex_lock(&amp;mutex);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">while</span> (bo-&gt;num == BUFFSIZE)&#123;</span><br><span class="line">            <span class="comment">//满等待互斥锁</span></span><br><span class="line">            pthread_cond_wait(&amp;full,&amp;mutex);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">//P</span></span><br><span class="line">        sem_wait(&amp;semempty);</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;当前工作进程为生产者2\n&quot;</span>);</span><br><span class="line">        <span class="keyword">char</span> c = retChar();</span><br><span class="line"></span><br><span class="line">        bo-&gt;end = (bo-&gt;end+<span class="number">1</span>)%BUFFSIZE;</span><br><span class="line">        bo-&gt;product[bo-&gt;end] = c;</span><br><span class="line">        bo-&gt;num++;</span><br><span class="line"></span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;生产字符为:%c\n&quot;</span>,c);</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;当前缓冲区数据个数为:%d\n&quot;</span>,bo-&gt;num);</span><br><span class="line"></span><br><span class="line">        pTime();</span><br><span class="line">        sem_post(&amp;semfull);</span><br><span class="line">        <span class="keyword">if</span>(bo-&gt;num == <span class="number">1</span>)&#123;</span><br><span class="line">            pthread_cond_signal(&amp;empty);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">//释放锁</span></span><br><span class="line">        pthread_mutex_unlock(&amp;mutex);</span><br><span class="line">        sleep(rand()%<span class="number">2</span>);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> *<span class="title">consumerOne</span><span class="params">(<span class="keyword">void</span> *args)</span></span>&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">BUFFER</span> *<span class="title">bo</span>;</span></span><br><span class="line">    bo = (struct BUFFER *) args;</span><br><span class="line">    <span class="comment">//缓冲区物品为0,等待empty条件 获取锁</span></span><br><span class="line">    <span class="keyword">while</span> (bo-&gt;num == <span class="number">0</span>)&#123;</span><br><span class="line">        pthread_cond_wait(&amp;empty,&amp;mutex);</span><br><span class="line">    &#125;</span><br><span class="line">    sem_wait(&amp;semfull);</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;当前工作进程为:消费者1\n&quot;</span>);</span><br><span class="line"></span><br><span class="line">    <span class="comment">//消费数据</span></span><br><span class="line">    bo-&gt;head = (bo-&gt;head+<span class="number">1</span>)%BUFFSIZE;</span><br><span class="line">    <span class="keyword">char</span> c = bo-&gt;product[bo-&gt;head];</span><br><span class="line">    bo-&gt;product[bo-&gt;head] = <span class="string">&#x27; &#x27;</span>;</span><br><span class="line">    bo-&gt;num--;</span><br><span class="line"></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;消费的字符为:%c\n&quot;</span>,c);</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;当前缓冲区数据个数为:%d\n&quot;</span>,bo-&gt;num);</span><br><span class="line">    pTime();</span><br><span class="line">    sem_post(&amp;semempty);</span><br><span class="line">    <span class="comment">//唤醒</span></span><br><span class="line">    <span class="keyword">if</span>(bo-&gt;num == BUFFSIZE<span class="number">-1</span>)&#123;</span><br><span class="line">       pthread_cond_signal(&amp;full);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="comment">//解开互斥锁</span></span><br><span class="line">    pthread_mutex_unlock(&amp;mutex);</span><br><span class="line">    sleep(rand()%<span class="number">2</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> *<span class="title">consumerTwo</span><span class="params">(<span class="keyword">void</span> *args)</span></span>&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">BUFFER</span> *<span class="title">bo</span>;</span></span><br><span class="line">    bo = (struct BUFFER *) args;</span><br><span class="line">    <span class="keyword">while</span> (bo-&gt;num == <span class="number">0</span>)&#123;</span><br><span class="line">        pthread_cond_wait(&amp;empty,&amp;mutex);</span><br><span class="line">    &#125;</span><br><span class="line">    sem_wait(&amp;semfull);</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;当前工作进程为:消费者2\n&quot;</span>);</span><br><span class="line"></span><br><span class="line">    <span class="comment">//消费数据</span></span><br><span class="line">    bo-&gt;head = (bo-&gt;head+<span class="number">1</span>)%BUFFSIZE;</span><br><span class="line">    <span class="keyword">char</span> c = bo-&gt;product[bo-&gt;head];</span><br><span class="line">    bo-&gt;product[bo-&gt;head] = <span class="string">&#x27; &#x27;</span>;</span><br><span class="line">    bo-&gt;num--;</span><br><span class="line"></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;消费的字符为:%c\n&quot;</span>,c);</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;当前缓冲区数据个数为:%d\n&quot;</span>,bo-&gt;num);</span><br><span class="line">     pTime();</span><br><span class="line">        sem_post(&amp;semempty);</span><br><span class="line">        <span class="keyword">if</span>(bo-&gt;num == BUFFSIZE<span class="number">-1</span>)<span class="comment">//消费者消费掉一个产品，就可以唤醒生产者了</span></span><br><span class="line">        &#123;</span><br><span class="line">            pthread_cond_signal(&amp;full);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="comment">//解开互斥锁</span></span><br><span class="line">        pthread_mutex_unlock(&amp;mutex);</span><br><span class="line">        sleep(rand()%<span class="number">2</span>);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span>&#123;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;生产者消费者问题:&quot;</span>);</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> <span class="title">BUFFER</span> *<span class="title">bo</span>;</span></span><br><span class="line">    bo = (struct BUFFER *)<span class="built_in">malloc</span>(<span class="keyword">sizeof</span>(struct BUFFER));</span><br><span class="line">    bo-&gt;head = bo-&gt;end = BUFFSIZE<span class="number">-1</span>;</span><br><span class="line">    bo-&gt;num = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">pthread_t</span> pid1,child1,pid2,child2;</span><br><span class="line"></span><br><span class="line">    sem_init(&amp;semempty, <span class="number">0</span>, BUFFSIZE);</span><br><span class="line">    sem_init(&amp;semfull, <span class="number">0</span>, <span class="number">0</span>);</span><br><span class="line">    <span class="comment">//创建线程</span></span><br><span class="line">    pthread_create(&amp;pid1, <span class="literal">NULL</span>, producerOne, (<span class="keyword">void</span> *) bo);</span><br><span class="line">    pthread_create(&amp;child1, <span class="literal">NULL</span>, consumerOne, (<span class="keyword">void</span> *) bo);</span><br><span class="line">    pthread_create(&amp;pid2, <span class="literal">NULL</span>, producerTwo, (<span class="keyword">void</span> *) bo);</span><br><span class="line">    pthread_create(&amp;child2, <span class="literal">NULL</span>, consumerTwo, (<span class="keyword">void</span> *) bo); </span><br><span class="line">    <span class="comment">//等待子线程</span></span><br><span class="line">    pthread_join(pid1, <span class="literal">NULL</span>);</span><br><span class="line">    pthread_join(child1, <span class="literal">NULL</span>);</span><br><span class="line">    pthread_join(pid2, <span class="literal">NULL</span>);</span><br><span class="line">    pthread_join(child2, <span class="literal">NULL</span>);</span><br><span class="line">    <span class="comment">//销毁信号量</span></span><br><span class="line">    sem_destroy(&amp;semfull);</span><br><span class="line">    sem_destroy(&amp;semfull);</span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>​    其中首先创建缓冲区结构体存取数据，然后pthread_t声明4个线程标识符，然后sem_init初始化信号量，三个参数分别为传入的信号量名，线程共享量，以及初始化大小即可用资源数目。pthread_create创建4个线程，参数传入缓冲区指针。然后各个线程进行各自操作，最后等待子线程分别完成即可。最后销毁信号量。</p>

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